Since successful industrial application of lasers is strongly dependent upon the success of light deflection technology, much effort has been directed at this problem. The results of this effort can be generally broken down into two classes, acoustic deflectors and mechanical deflectors. The acoustic deflectors are limited in spatial spanning capacity whereas the mechanical deflectors are limited in speed. A disclosure of a mechanical deflector employing a multi-faceted rotating polygon was found in the recently-issued U.S. Pat. No. 3,995,110.
In August of 1974 Pole et al disclosed a holographic laser beam deflector (IBM Research Paper RJ 1423). This deflector comprises several transmission type volume holograms recorded on a cylindrical surface. A reconstructing laser beam having a virtual source at the center of rotation of the cylinder illuminates the hologram which then deflects the illuminating beam in a scanning type motion. The deflecting hologram is produced through the interference of a pair of coherent laser beams at a cylindrical surface having rotational symmetry with respect to an axis containing the origin of one of the beams. For deflection purposes, the illuminating source, also located at the center of symmetry, has a reduced aperture, and the hologram produces a scanning light beam as the cylindrical surface is rotated.
There are a number of parameters which determine the utility of a deflector of this sort, one of which is the resolution of the resulting scanning beams, i.e., how many different resolvable spots can be produced in a given scan field?
One difficulty inherent in the Pole et al approach is that since the co-action of hologram and illuminating beam is to recreate the object beam, the scan field traces out a circle, or circular arc, as the hologram rotates. While for some applications such a scanning field is desirable, the typical scanning application requires a flat or nearly flat field scan. The circular scan of the Pole et al device can, of course, be corrected by optics, but this is only at the expense of resolution and/or scan width.
It is therefore one object of the present invention to provide a light deflector having the advantages of the Pole et al device, while, at the same time, producing a flat field or nearly flat field scan. It is another object of the present invention to provide a holographic light deflector which illustrates increased resolution over the prior art holographic light deflectors, such as computer generated holograms. It is another object of the present invention to provide a light deflector having advantages of prior art holographic light deflectors while, at the same time, providing for flat or nearly flat field scan.